title: SUMO-1 modification and its role in targeting the Ran GTPase-activating protein, RanGAP1, to the nuclear pore complex.
abstract: RanGAP1 is the GTPase-activating protein for Ran, a small ras-like GTPase involved in regulating nucleocytoplasmic transport. In vertebrates, RanGAP1 is present in two forms: one that is cytoplasmic, and another that is concentrated at the cytoplasmic fibers of nuclear pore complexes (NPCs). The NPC-associated form of RanGAP1 is covalently modified by the small ubiquitin-like protein, SUMO-1, and we have recently proposed that SUMO-1 modification functions to target RanGAP1 to the NPC. Here, we identify the domain of RanGAP1 that specifies SUMO-1 modification and demonstrate that mutations in this domain that inhibit modification also inhibit targeting to the NPC. Targeting of a heterologous protein to the NPC depended on determinants specifying SUMO-1 modification and also on additional determinants in the COOH-terminal domain of RanGAP1. SUMO-1 modification and these additional determinants were found to specify interaction between the COOH-terminal domain of RanGAP1 and a region of the nucleoporin, Nup358, between Ran-binding domains three and four. Together, these findings indicate that SUMO-1 modification targets RanGAP1 to the NPC by exposing, or creating, a Nup358 binding site in the COOH-terminal domain of RanGAP1. Surprisingly, the COOH-terminal domain of RanGAP1 was also found to harbor a nuclear localization signal. This nuclear localization signal, and the presence of nine leucine-rich nuclear export signal motifs, suggests that RanGAP1 may shuttle between the nucleus and the cytoplasm.
authors.affiliation: Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York 10021, USA. Matunim@rockvax.rockefeller.edu
authors.forename: M J
authors.initials: MJ
authors.lastname: Matunis
authors.forename: J
authors.initials: J
authors.lastname: Wu
authors.forename: G
authors.initials: G
authors.lastname: Blobel
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D006367:HeLa Cells; D006801:Humans; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000378:metabolism*; D019913:Nuclear Localization Signals; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D025842:SUMO-1 Protein; D017384:Sequence Deletion; D014452:Ubiquitins / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D020690:GTPase-Activating Proteins; D018832:Molecular Chaperones; D019913:Nuclear Localization Signals; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; C092317:RANGAP1 protein, human; D011994:Recombinant Proteins; D025842:SUMO-1 Protein; D014452:Ubiquitins; C094493:ran-binding protein 2